1. Field of the Invention
The present patent application for industrial invention relates to an engine sound enhancement (ESE) system of a vehicle.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
As it is known, most vehicles are provided with an internal combustion engine. Each internal combustion engine is characterized by a typical sound, according to its structure, horsepower and piston displacement. Generally, each car manufacturer is distinguished by a typical engine sound.
In order to improve passenger comfort and make the vehicle as noiseless as possible, vehicle compartments are acoustically insulated from the hood that contains the engine. Consequently, the car driver inside the compartment cannot hear the engine sound while driving. Such a noiseless condition of the vehicle results in some drawbacks, especially in the case of sports cars, for which it is useful for the driver to hear the engine sound in order to decide a driving style.
U.S. Pat. No. 7,203,321 discloses a sound enhancing system comprising:                a sound pressure sensor positioned proximal to or within one of an intake tract and an exhaust tract of the motor to detect the motor sound pressure,        a signal processing unit that processes the signal of the sound pressure sensor,        a synthesizer that outputs a synthesized signal,        an adder that adds the signal from the sound pressure sensor to the synthesizer signal and sends the output signal to a speaker that generates an enhancing sound.        
Nevertheless, said system is not effective, especially because the sound pressure sensor is disposed in the intake tract or in the exhaust tract and is not capable of detecting the real motor sound accurately because said sound pressure sensor only considers the sound generated by the sound pressure that propagates in the intake tract or in the exhaust tract, without considering the real sound caused by the vibration of the motor casing.
For this reason, the audio signal generated only by the sound pressure sensor is not satisfactory in order to reproduce the real motor sound. It is therefore necessary to use a synthesizer and generate a (completely artificial) synthesized signal that is added to the sound pressure signal detected by the sound pressure sensor. Evidently, the artificial sound generated from the synthesized signal can never be identical to the real motor sound.
U.S. Pat. No. 8,300,842 discloses a noise enhancement system of the engine, comprising:                a speaker for generating a noise enhancement signal; and        a controller that controls the speaker with a control signal corresponding to the noise enhancement signal.        
The controller receives only one signal indicative of the engine speed, which is obtained from a vehicle tachometer, and adds additional values to said engine speed signal for calculating the control signal based upon a predicted future engine sound. The predicted future engine sound is determined using the input signal from the vehicle tachometer and a value derived from the input signal from the vehicle tachometer indicative of engine angular acceleration.
Also this system is not very accurate because it generates a completely artificial signal based on values obtained from the tachometer and processed by means of a complex algorithm; moreover, it does not take into account the real sound generated by the engine.
Engine sound enhancement systems are known, comprising a plurality of microphones disposed in various parts of the vehicle and a mixer that mixes the signals coming from said microphones. A plurality of sensors continuously detects the driving conditions of the vehicle and controls the gain of the signals from said microphones. In order to operate these systems need a plurality of microphones and are therefore expensive, complicated and cumbersome.